Basic Ergonomics Product Audit Shambu Nandanan

Carpenter’s HammerTask Objective

The task objective is multi functional. It may be hammering a nail into wood during carpentry or into walls for other utility functions.

Tool Description

The head of a hammer is made from a strong and heavy metal (normally steel or iron). It has a flat hitting surface which acts as the point of contact, in this case, with the nail. The more sophisticated hammers have a titanium head which offers a reduced amount of recoil and thus results in greater efficiency and reduced fatigue.

The handle length ranges from 13 to 18 inches. If the handle is too long, the force generated will be to the wrong place and thus off target. If it is too short, then not enough force will be generated by each blow. The handle of the hammer is designed to keep a safe distance of the user’s hand from the impact point. It is wide and thick enough to comfortably fit inside the clenched hand while providing a tight grip. This helps to maximize the speed and accuracy of the blows delivered.

The full weight of a household utility hammer may be anywhere between 350 to 750 grams. The larger portion of the weight is on the hammer head to increase the force generated by each blow.

Usage Environment

The carpenter’s hammer is used on various surfaces like wood, plaster, concrete, rubber, cardboard, thin metal etc. The nail used should be chosen to suit the surface as some surfaces may require more force and thus, more resilient nails.

Body Parts in Play

Performing this function requires the use of the dominant hand for the hammer and the other hand for holding the nail in place. The elbow has to be kept steady to ensure that the swing is smooth and precise. The grip on the hammer must be firm enough to ensure that the hammer is securely held in place, but not too tightly so that

the hand does not absorb too much of the force that is generated by the hammer’s recoil after striking the nail head.

The wrist has to be held tightly as well to prevent inaccuracy while striking and also to prevent any form of muscle injury. A notable part of the work is also distributed across the forearm, bicep and deltoids as well while performing this action.

Action Dynamics

The hammer is always held in the dominant hand while the other hand is used to hold the nail at an angle perpendicular to the surface. The hammer is then swung in a circular arc by using the elbow as a pivot. The hammer head has to strike the head of the nail at the same angle of the nail and the surface, to ensure the most

effectiveness. The speed of the swing and the length of the swing arc determine the amount of force with which the nail will be driven into the surface.

Operation Time and Frequency

Hammering requires the same action to be repeated successively for a certain number of times depending upon the strength of the blow, the surface and the nail quality. Hammering a nail into a wooden block may require 7 – 10 blows while if it is into a concrete surface about 15 – 20 blows might be required. Softer surfaces like cardboard, plywood and rubber may require only 3 – 5 strong strikes.

The task of driving one nail into the surface may take anywhere between 10 seconds and a minute depending on the toughness of the surface, the skill level of the user and the quality of the equipment used.

Effects on the body

In carpentry, the completion of one carpentry task may require several pieces to be nailed together and so a lot of hammering goes into a carpenter’s daily routine. This means that the entire portion of his dominant arm, right from the shoulder is in constant use and so may be subject to a lot of strain. While observing a carpenter for this study, it was noticed that his right arm (being his dominant one) had a notably larger muscle build and tone than his left arm. Many different tasks may contribute to this difference, but with the high frequency of hammer use in his daily routine, the role of the hammer in this development can be said to be a significant one.

Hand eye coordination is another essential requirement in the performance of this task. The force at which the hammer is swung can seriously damage the hand holding the nail, if not carefully executed. As observed with the carpenter, this action, however, becomes an easy one through constant practice and application. The degree of confidence and ease with which he was performing this task showed that it was not one of the more daunting parts of his profession.

This task cannot be performed continuously for a long period of time. Even the carpenter who has achieved a certain level of expertise in this function cannot continue it for more than 10 minutes at a stretch. It deals a lot of stress on the wrist, the biceps and the forearm due to the force with which the hammer is swung and because of the recoil from the strike. The tight grip on the handle also becomes uncomfortable after prolonged use.